Continuously optimized solar cell metallization design through feed-forward process

ABSTRACT

An improved, lower cost method of processing substrates, such as to create solar cells, is disclosed. The doped regions are created on the substrate, using a mask or without the use of lithography or masks. After the implantation is complete, visual recognition is used to determine the exact region that was implanted. This information can then be used by subsequent process steps to crate a suitable metallization layer and provide alignment information. These techniques can also be used in other ion implanter applications. In another aspect, a dot pattern selective emitter is created and imaging is used to determine the appropriate metallization layer.

BACKGROUND OF THE INVENTION

Solar cells are typically manufactured using the same processes used forother semiconductor devices, often using silicon as the substratematerial. A semiconductor solar cell is a device having an in-builtelectric field that separates the charge carriers generated through theabsorption of photons in the semiconductor material. This electric-fieldis typically created through the formation of a p-n junction (diode)which is created by differential doping of the semiconductor material.Doping a part of the semiconductor substrate (e.g. surface region) withimpurities of opposite polarity forms a p-n junction that may be used asa photovoltaic device converting light into electricity.

FIG. 1 shows a cross section of a representative substrate 100,comprising a solar cell. Photons 101 enter the solar cell 100 throughthe top surface 105, as signified by the arrows. These photons passthrough an anti-reflective coating 110, designed to maximize the numberof photons that penetrate the substrate 100 and minimize those that arereflected away from the substrate.

Internally, the substrate 100 is formed so as to have a p-n junction120. This junction is shown as being substantially parallel to the topsurface 105 of the substrate 100 although there are otherimplementations where the junction may not be parallel to the surface.The solar cell is fabricated such that the photons enter the substratethrough the n-doped region, also known as the emitter 130. While thisdisclosure describes p-type bases and n-type emitters, n-type bases andp-type emitters can also be used to produce solar cells and are withinthe scope of the disclosure. The photons with sufficient energy (abovethe bandgap of the semiconductor) are able to promote an electron withinthe semiconductor material's valence band to the conduction band.Associated with this free electron is a corresponding positively chargedhole in the valence band. In order to generate a photocurrent that candrive an external load, these electron-hole (e-h) pairs need to beseparated. This is done through the built-in electric field at the p-njunction. Thus any e-h pairs that are generated in the depletion regionof the p-n junction get separated, as are any other minority carriersthat diffuse to the depletion region of the device. Since a majority ofthe incident photons are absorbed in near surface regions of the device,the minority carriers generated in the emitter need to diffuse acrossthe depth of the emitter to reach the depletion region and get sweptacross to the other side. Thus to maximize the collection ofphoto-generated current and minimize the chances of carrierrecombination in the emitter, it is preferable to have the emitterregion 130 be very shallow.

Some photons pass through the emitter region 130 and enter the base 140.These photons can then excite electrons within the base 140, which arefree to move into the emitter region 130, while the associated holesremain in the base 140. As a result of the charge separation caused bythe presence of this p-n junction, the extra carriers (electrons andholes) generated by the photons can then be used to drive an externalload to complete the circuit.

By externally connecting the emitter region 130 to the base 140 throughan external load, it is possible to conduct current and thereforeprovide power. To achieve this, contacts 150, typically metallic, areplaced on the outer surface of the emitter region 130 and the base 140.Since the base 140 does not receive the photons directly, typically itscontact 150 b is placed along the entire outer surface. In contrast, theouter surface of the emitter region 130 receives photons and thereforecannot be completely covered with contacts. However, if the electronshave to travel great distances to the contact, the series resistance ofthe cell increases, which lowers the power output. In an attempt tobalance these two considerations; the distance that the free electronsmust travel to the contact, and the amount of exposed emitter surface160; most applications use contacts 150 a that are in the form offingers. FIG. 2 shows a top view of the solar cell of FIG. 1. Thecontacts are typically formed so as to be relatively thin, whileextending the width of the solar cell. In this way, free electrons neednot travel great distances, but much of the outer surface of the emitteris exposed to the photons. Typical contact fingers 150 a on the frontside of the wafer are between 40 μm and 200 μm. These fingers 150 a aretypically spaced between 2-3 mm apart from one another. While thesedimensions are typical, other dimensions are possible and contemplatedherein.

A further enhancement to solar cells is the addition of heavily dopedsubstrate contact regions. FIG. 3 shows a cross section of this enhancedsolar cell. The cell is as described above in connection with FIG. 1,but includes heavily n-doped contact regions 170. These heavily dopedcontact regions 170 correspond to the areas where the metallic fingers150 a will be affixed to the substrate 100. The introduction of theseheavily doped contact regions 170 allows much better contact between thesubstrate 100 and the metallic fingers 150 a and significantly lowersthe series resistance of the cell. This pattern of including heavilydoped regions on the surface of the substrate is commonly referred to asselective emitter design. These heavily doped regions may be created byimplanting ions in these regions. Thus, the terms “implanted region” and“doped region” may be used interchangeably throughout this disclosure.

A selective emitter design for a solar cell also has the advantage ofhigher efficiency cells due to reduced minority carrier losses throughrecombination due to lower dopant/impurity dose in the exposed regionsof the emitter layer. The higher doping under the contact regionsprovides a field that collects the majority carriers generated in theemitter and repels the excess minority carriers back toward the p-njunction.

In addition to selective emitter designs, other solar cell designsrequire patterned doping. Another example is the interdigitated backcontact (IBC) cell, which requires offset patterns of n-type and p-typedopants on the back side of the cell.

Such structures are typically made using traditional lithography (orhard masks) and thermal diffusion. An alternative is to use implantationin conjunction with a traditional lithographic mask, which can then beremoved easily before dopant activation. Yet another alternative is touse a shadow mask or stencil mask in the implanter to define the highlydoped areas for the contacts. All of these techniques utilize a fixedmasking layer (either directly on the substrate or in the beamline).

All of these alternatives have significant drawbacks. For example, theprocesses enumerated above all contain multiple process steps. Thiscauses the cost of the manufacturing process to be prohibitive and mayincrease wafer breakage rates. These options also suffer from thelimitations associated with the special handling of solar wafers, suchas aligning the mask with the substrate and the cross contamination withmaterials that are dispersed from the mask during ion implantation.

FIG. 4 shows the typical processing steps required to create patterneddoping using a shadow or proximity mask. In step 400, the solar cell isdesigned. This includes creating the dopant patterns and metallizationlayers. Based on the desired dopant patterns, a matching proximity maskis design (step 410). Pre-implant manufacturing processes are performed(step 420). For example, in some embodiments, the wafers arrive at thefactory as raw sawn wafers. The first step on entering the factory isinspection. The wafers are checked for cracks, resistivity & size. Afterthat, the wafer may go into a series of wet benches. The first wet stepmay be to remove the saw damage from the wafers. This is typically a 10um etch from both sides of the wafer to remove the micro-cracks formedby sawing. The next step may be an anisotropic etch that forms therandom pyramid texturing on the wafer surfaces. This may help lighttrapping. The pre-processed wafer is then physically aligned within theion implanter (step 430). This step also includes precise positioning ofthe proximity mask. The ion implant of the wafer is then performed, withthe proximity mask in place (step 440). After the wafer has beenimplanted, various post-processing steps, such as anneal and SiN_(x)deposition, are performed on it (step 450). The wafer is aligned withrespect to a reference edge or indicia prior to application of themetallization pattern (step 460). Finally, the metal layer is applied tothe wafer (step 470). In the case of a solar cell, the metal layer istypically applied atop the heavily doped regions of the wafer (i.e.those regions implanted during implantation step 440). The final step offabricating a solar cell is the firing step, where the printed metal isdriven in to the cell to make the actual contacts.

However, there are many known problems with the use of a proximity mask,especially in solar cell applications. FIG. 5 shows a wafer 501 beingimplanted by an ion beam 502, through a proximity mask 503. The mask 503has a plurality of slots, where each is separated from the adjacentslots by a slot-location spacing 500. The first of these slots is offsetfrom an indicia 504 by a distance 510. The mask 503 has a certainthickness (t) and is offset vertically above the wafer 501 by a gap. Asshown in FIG. 5, the ion beam 502 may not be completely orthogonal tothe wafer 501. The beam angle (θ), the mask thickness (t) and the gapfrom the mask 503 to the wafer 501 all have an effect on the location ofthe implanted regions 505. For example, the greater the gap between themask 503 and the wafer 501, the more lateral displacement between thedesired implant region and the actual implant region 505. Similarly, athicker mask will tend to reduce the overall width of the implantedregion 505, to a width less than the slot width 520. In addition, theuse of a proximity mask 503 requires multiple alignment steps. First,the mask 503 must be aligned with the wafer 501. Subsequently, the metallayer has to be aligned as well. FIG. 5 shows the metal 506 applied inthe desired location. However, the variability of the steps creates asituation where the metal 506 is not applied over the center of theimplanted region 505. The offset from the implanted region 505 to themetal 506 is referred to as feature error, and is shown as beingpositive on the left side of the implanted region 505 and negative onthe right side of the implanted region 505.

In summary, proximity masks can cause the following problems:

-   -   Variability of desired feature placement due to machining        tolerances;    -   Variability of feature placement due to incident ion beam angle        accuracy (resulting from mask gap or ion beam repeatability);    -   Variability of feature placement due to wafer positioning;    -   Variability of feature placement due to wafer size tolerances;        and    -   Tight alignment requirement for the application of        metallization.

To accommodate these system tolerances, often the implanted region 505is larger in size than optimally desired. In the case of selectiveemitter cells, the oversized implanted regions 505 expand into theemitter region, thereby reducing the surface area of the emitter region.This results in a lower cell efficiency.

FIGS. 6A-C show the impact of these wider implanted regions on a solarcell 600. FIG. 6A shows a typically geometry of a solar cell withbusbars 605 and metal fingers 610. FIG. 6B is an expanded view of aportion of FIG. 6A, showing the metal fingers 610, busbar 605 andimplanted regions 615 in more detail. To insure that the metal fingers610 and busbars 605 do not cover the emitter region 620, the implantedregions 615 are created with a greater width than desired. Note that anyarea which is implanted and not covered by metal is less efficient incapturing solar energy.

FIG. 6C shows a section view of an existing process. The metal finger610 is located at the leftmost position, based on known tolerances. Toinsure that the metal finger 610 does not contact the emitter region620, the implanted region 615 is made wide enough such that in allscenarios, with maximum tolerances and minimum widths, the metal fingeris covering only implanted region 615. However, the exposed portions ofimplanted region 615 are less efficient in capturing solar energy.

In addition, high precision alignment systems and the above describedproduction method is inherently costly. Consequently, efforts have beenmade to reduce the cost and effort required to dope a pattern onto asolar cell.

Therefore, there exists a need to produce solar cells where the numberand complexity of the process steps is reduced, while maintainingadequate accuracy so that subsequent process steps are correctlypositioned. While applicable to solar cells, the techniques describedherein are applicable to other doping applications.

SUMMARY OF THE INVENTION

An improved, lower cost method of processing substrates, such as tocreate solar cells, is disclosed. The doped regions are created on thesubstrate, such as using a mask. In other embodiments, the doped regionsare created without the use of lithography or masks. After theimplantation is complete, visual recognition is used to determine theexact region that was implanted. This information can then be used bysubsequent process steps to crate a suitable metallization layer andprovide alignment information. These techniques can also be used inother ion implanter applications.

In another aspect, a dot pattern selective emitter is created andimaging is used to determine the appropriate metallization layer.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a cross section of a solar cell of the prior art;

FIG. 2 shows a top view of the solar cell of FIG. 1;

FIG. 3 shows a cross section of a solar cell using selective emitterdesign;

FIG. 4 shows a production flowchart of the prior art;

FIG. 5 shows the sources of inaccuracy with a proximity mask;

FIGS. 6A-C show the relative widths and positions of implanted regionsand metal layers according to the prior art;

FIG. 7A is a flowchart of the manufacturing process in accordance withone embodiment;

FIG. 7B is a flowchart of the manufacturing process in accordance with asecond embodiment;

FIG. 8 is an expanded view of an implanted wafer;

FIG. 9 is the wafer of FIG. 8 with a metal layer applied;

FIG. 10 is a dot collector grid for a solar cell; and

FIG. 11 is the solar cell of FIG. 10 with metal linkages applied.

DETAILED DESCRIPTION OF THE INVENTION

As described above, current manufacturing processes require precisealignment of implanted regions on the solar cell with the metallizationlayer. By eliminating this requirement for precision, the manufacturingprocess can be simplified and made more cost effective.

To reduce this complexity, an image, such as a high resolution image, ofthe wafer is obtained after the wafer has been implanted. This image maybe taken at various points in the process. For example, the image may betaken immediately after ion implantation, after activation (wither withor without oxidation), or after passivation with SiN_(x). The point inthe process at which the image is taken may determine how clearly theimplanted regions can be detected. The implanted regions can bedifferentiated from emitter regions on a high resolution image. Thisimage is then processed to determine the position and sizes of theimplanted features. Based on this processing, a metallization layer canbe prepared. This metallization layer, which corresponds to thethickness and position of the implanted regions, is then applied to thewafer in a subsequent processing step. In this way, the efficiency ofthe solar cell is increased, as the emitter region can be maximized.

FIG. 7A shows a flowchart of one embodiment. Similar to the currentprocesses, the parametric solar cell design is completed (step 700). Insome embodiments, a metallization pattern is also generated at thistime. The design of a matching proximity mask, based on the solar cellpattern is also created (step 705). These two components are used inpre-implant manufacturing processes (step 710). The wafer is thenaligned in the ion implanter (step 715). This alignment need not be asprecise as the alignment in the prior art (step 430). In the prior art,the subsequent processing steps were all based on alignment to knownindicia or fiducials. Therefore, it was critical that all processes betightly aligned to these indicia, to minimize variation. However, in thepresent embodiment, the subsequent steps are based on the indicia andthe high-resolution image of the implanted regions. Thus, any variationin position of the implanted region with respect to the indicia orfiducials can be captured and compensated for later in the process.

In step 720, the wafer is implanted by the ion implanter with theproximity mask located in front of the wafer. This implantation stepcreates the implanted regions onto which the metal is to be applied. Itshould be noted that other methods of selectively implanting the wafermay also be used. For example, other methods such as sheath engineering,modulation of the ion beam, and movement of the workpiece during ionimplantation, can also be used to create a implant pattern in the wafer.

After implantation, an image, such as a high-resolution image, of theimplanted wafer is obtained (step 725). This high resolution image canbe obtained by any suitable means, including a CCD camera, electron beam(SEM), Auger Emission spectroscopy, an infrared camera, a photodiode,secondary ion mass spectroscopy (SIMS), surface contact resistance,photoluminence, a laser (such as Thermawave) or other systems. Thus, theterm “image” is used to describe the pattern which indicates therelative placement of the implanted regions on the wafer, regardless ofthe means used to generate that pattern.

The high resolution image is then processed to determine the edges ofthe implanted regions, and to determine the overall pattern of theimplanted region (step 730). The high-resolution image may be associatedwith the wafer, such as through an identifier and other characterizingmark. The image is processed by a computing device or controller. Thecontroller has a processing unit, capable of executing instructions, anda memory device. The memory device typically contains computer readableand executable instructions, as well as other information. Theexecutable instructions comprise the metallization algorithm. The memorymay contain both volatile and non-volatile portions. The controller mayinclude other functions, such as input/output ports, sensors, and otherdevices.

This information is then supplied to a metallization algorithm to definethe specific shape of the metal pattern for this particular wafer. Suchan algorithm is typically executed on a controller or computing device.The algorithm may be executed on the same controller as used for theimage processing. In other embodiments, a different controller isutilized for the metallization algorithm.

The resulting data may be stored in a database, associated with thewafer identification. In this way, subsequent process steps can querythe database to determine the appropriate measurements and setting to beused with a particular wafer.

After the high resolution image has been taken, the wafer is thensubjected to post-implant processes (step 735).

The metallization algorithm determines the specific shape of the metalpattern. In some embodiments, the metal pattern is determined toaltering the parameters of a pre-existing pattern (step 745). In thisembodiment, the algorithm utilizes the predefined metallizationparameters (step 740) as a initial draft of the metal pattern. Based onthe image processing, the algorithm may increase or decrease certainpredetermined parameters. For example, the width of the metal layer maybe altered based on the actual measured thickness of the implantedregions. Similarly, metal-metal location 560 (see FIG. 5) may be alteredbased on actual placement of the implanted regions.

In other embodiments, the metallization algorithm creates a new metalpattern by offsetting the edges of the implant region (step 750). FIG. 8shows an expanded view of a portion of the top surface of a solar cell,after the wafer has been implanted (step 720). At this point in theprocess, implanted regions 815 have been created amid emitter region820. The high resolution image determines the outline of the implantedregions 815 and creates a metallization layer, based on the actual sizeand shape of the implanted regions 815. In some embodiments, the metallayer is made slightly thinner than the underlying implanted regions 815to allow for tolerances and inaccuracies in the alignment process. Ametal layer, such as that shown in FIG. 9, is then created by thealgorithm, and is subsequently applied.

In other embodiments, as shown in FIG. 7B, the metal layer is depositedthrough the use of inkjet printing technology. Ink jet printers ejectmodulated droplets of liquid through an array of nozzles onto a surface,such as a surface of a solar cell 100. The nozzles may be controlled by,for example, a piezo electric motor or other methods known to thoseskilled in the art. The surface may be scanned across this array ofnozzles, though the array of nozzles may be scanned as well. The patternused by the inkjet printer can be created based on the high resolutionimage taken in step 725. Based on the image, a metallization pattern forthe inkjet printer can be created, as shown in step 770. In this way,the inkjet nozzles can deposit metal exactly on top of the implantedregions, as shown in FIG. 9.

Regardless of the method used, the metal layers are typically appliedlater in the production process. It may therefore be necessary tore-align the wafer to its initial position (from step 720). To do this,the wafer may be uniquely identified, such as by using position orcharacterizing marks on the wafer. Returning to FIGS. 7A-B, a secondimage is taken of the wafer (step 755) to obtain its position. In someembodiments, its position is measured relative to a fixed indicia orfiducial. The wafer is then aligned to the indicia to return it to theexact location that it was in during the initial implant (step 760).These steps may be performed by a positioning system comprising anoptical sensor and a motion control stage. Having determined andadjusted the position of the wafer, the wafer is then printed with ametal paste using a suitable method (step 765). The most commonly usedmethod is screen printing. Ink jet printing, as shown in FIG. 7B, mayalso be used a non-contact printing method, which improves wafer yielddue to less breakage, as shown in step 775. Aerosol sprays may also beused. FIG. 9 shows the wafer after the metal layer 805, 801 have beenapplied. Note that the ratio of the width of the metal layer to thewidth of the implanted region is much greater than was possible in theprior art (see FIG. 6B). In the prior art, implanted regions having awidth of 500 μm are used in conjunction with 110 μm metal lines. This isa ratio of about 20%. Using present printing methods, the placement ofthe metal line may be controlled to about 15 μm. Thus, for a 110 μmmetal line, the implanted region only needs to be about 140 μm toguarantee that the metal line is applied atop the implanted region.Similarly for a 40 μm metal line, the implanted region only needs to beabout 70 μm. The ratio of these widths varies with the desired metalline width and can be greater than 50%. In the case of 110 μm metallines, this ratio can be greater than 75%.

The tolerance of the placement of the metal lines limits the ratio thatcan be achieved. As described above, currently, the placement of themetal lines can be controlled to about 15 μm. Thus, the width of themetal line, added to twice this tolerance establishes the minimum widthfor the implanted region. Thus, as the placement tolerances are reduced,the ratio of metal line width to implanted region width can beincreased.

Although this process has been described in conjunction with selectiveemitter designs, the disclosure is not limited to this embodiment. Asdescribed above, interdigitated back contact (IBC) solar cells containheavier patterned implanted regions on the back side of the wafer. Theabove technique could be used to determine the exact location, width andshape of the p+ and n+ doped regions. Based on the images, metal layersfor each can be generated using the techniques described above (steps745 and 750). These metal patterns can then be applied to the back sideof the IBC solar cell.

In addition, this process has been described in conjunction with aproximity mask. However, this method can also be used with other methodsof selective implantation, such as sheath engineering. In all cases, theimplanted region is detected and the subsequent application of themetallization layer is modified based on the actual location of theimplanted regions.

Although some embodiments of solar cells use a pattern that includesbusbars and fingers, other configurations are also possible. FIG. 10shows the top surface of a solar cell 1000. In this embodiment,implanted regions 1010 are circular or nearly circular and arranged in agrid. For this selective emitter type application, the collector dots(i.e. implanted regions) are n++ implants (for a phosphorus implant).Typically there would also be a blanket emitter of n+ type. AlthoughFIG. 10 shows the implanted regions 1010 forming a regularly shaped andspaced grid, any arrangement of implanted regions is possible. In thisconfiguration, the metal layer comprises two components; the collectordots, which overlay the implanted regions 1010, and the interconnectswhich connect the various collector dots together.

The size, shape and location of the metal collectors can be createdusing the process described above. In this way, the metal collectors canbe formed so as to occupy as much of the implanted region as possible.

In addition to dot collectors on the top surface, this technique canalso be used on the back side of the solar cell. For example, a dotcollector may be used on the back side to create a back-surface field.

In addition to creating the metal collector pattern, the high resolutionimage can be used for other purposes. Unlike the configuration of FIG.6, the implanted regions can be connected in a variety of ways. Forexample, the metal collectors can be connected using a tree-likestructure, where individual collectors are linked by very thin wires(due to the limited amount of current being passed). As individualcollectors are linked, the metal collections become thicker, toaccommodate the increased current load.

FIG. 11 shows an example of a dot collector solar cell, where the metalcollectors 1010 are connected using metal wires. Note that wires whichconnect a single collector (i.e. 1020) are very thin, as the current isvery low from a single collector. As the currents from a plurality ofcollectors are linked, the metal connections need to increase in size aswell. Linkage 1020 connects a single collector, and therefore is verythin. Linkage 1025 connects two collectors and is therefore slightlythicker. Linkages 1027, 1028 are progressively thicker due to theincrease load through them. Ultimately, all of the collectors areconnected to a busbar 1030.

Smaller metal linkages (i.e. 1020) have a higher series resistancerelative to their presented shadow. A dot pattern selective emitter canbe designed to increase the current to increasingly larger linkages(i.e. 1027, 1028) while simultaneously minimizing the number of linkagesin the network. Based on the actual pattern of implanted regions, thealgorithm can optimize the placement and thickness of the linkagesconnecting the metal collectors. The controller makes these adjustmentbased on predetermined control parameters, governed by the actual metalplacement accuracy and other physical and electrical characteristics.

For example, a mask may create a first dot pattern. After the highresolution pattern has been created, a dynamic optimizing softwareprogram determined the location and size of each dot. Based on this, thesoftware program can generate an optimal set of linkages.

Over time, various effects can cause this optimized linkage pattern tochange.

For example, if the screen used for the implantation process is slightlyoffset relative to the wafer, all of the implanted dots will becorrespondingly offset. Since this is a change that affects all of thedots in a uniform manner, the optimal linkage pattern may not need to bechanged. However, each of the dots and linkages may also becorrespondingly offset.

In another example, if the screen used for the implantation process istilted, the placement and size of the dots may be affected. Assume thescreen is tilted such that it is closer to the wafer on the left side.Since the screen is closer to the wafer on this side, the implanted dotswill tend to be smaller as the beam expands less after passing throughthe screen. A tilt also affects the placement of the dots, bringing themcloser together. Thus, a tilted screen may affect both the size andlocation of the dots. Since the effect may not be uniform across theentire wafer, the optimal linkage may change.

In another example, if the screen wears out or warps, the implantedpattern will be affected. Often, this type of wear out affects theimplanted pattern in a non-uniform way. Therefore, the optimal linkagesmay change as a result of screen wearout.

By utilizing the high resolution image of the implanted regions tocreate an optimized linkage pattern, several benefits are achieved.First, there is greater tolerance as to the alignment of the mask to thewafer during implantation. Secondly, since imperfections due to maskwear out can be compensated for, the useful life of the mask can beincreased.

The present disclosure is not to be limited in scope by the specificembodiments described herein. Indeed, other various embodiments of andmodifications to the present disclosure, in addition to those describedherein, will be apparent to those of ordinary skill in the art from theforegoing description and accompanying drawings. Thus, such otherembodiments and modifications are intended to fall within the scope ofthe present disclosure. Further, although the present disclosure hasbeen described herein in the context of a particular implementation in aparticular environment for a particular purpose, those of ordinary skillin the art will recognize that its usefulness is not limited thereto andthat the present disclosure may be beneficially implemented in anynumber of environments for any number of purposes. Accordingly, theclaims set forth below should be construed in view of the full breadthand spirit of the present disclosure as described herein.

1. A method of applying a metallization layer to a substrate,comprising: implanting ions into a portion of said substrate, wherebysaid ions form a plurality of implanted regions, each having a minimumwidth; using a detection system to determine an actual location and awidth of said implanted regions; using said actual location to generatea metallization pattern, whereby said metallization pattern comprises aplurality of lines, each having a metallization width, wherein saidmetallization pattern is determined based on said width of saidimplanted regions and a placement tolerance of said metallizationpattern; and applying said metallization pattern to said substrate. 2.The method of claim 1, wherein said metallization pattern covers atleast 50% of said implanted regions.
 3. The method of claim 1, furthercomprising processing said substrate so as to produce a solar cell. 4.The method of claim 1, wherein said metallization width is determined bysubtracting twice said placement tolerance from said width of saidimplanted regions.
 5. The method of claim 1, wherein said metallizationpattern is applied by an inkjet printer.
 6. The method of claim 5,further comprising processing said substrate so as to produce a solarcell.
 7. The method of claim 1, wherein said detection system generatesan image of said substrate.
 8. The method of claim 7, further comprisingactivating said ions and passivating said substrate, wherein said imageis generated after said activating and said passivating.
 9. The methodof claim 1, wherein said using said actual location to generate saidmetallization pattern alters a preexisting metallization pattern. 10.The method of claim 1, wherein said metallization pattern covers lessthan 100% of said implanted regions.
 11. The method of claim 1, whereinsaid metallization pattern is specific to said substrate.
 12. An articleof manufacture comprising a storage medium containing instructions thatwhen executed enable a system to generate a metallization pattern afterreceiving an actual location and a width of a plurality of implantedregions, whereby said metallization pattern comprises a plurality oflines, each having a metallization width, and wherein said metallizationpattern is determined based on said width of said implanted regions anda placement tolerance of said metallization pattern; and communicatesaid metallization pattern to a processing unit configured to apply saidmetallization pattern to a substrate.
 13. The article of manufacture ofclaim 12, further comprising instructions that when executed enable asystem to generate said metallization pattern such that saidmetallization pattern covers at least 50% of said implanted regions. 14.The article of manufacture of claim 12, further comprising instructionsthat when executed enable a system to generate said metallizationpattern such that said metallization pattern covers less than 100% ofsaid implanted regions.
 15. The article of manufacture of claim 12,further comprising instructions that when executed enable a system togenerate said metallization pattern such that said metallization patternis specific to said substrate.
 16. The article of manufacture of claim12, further comprising instructions that when executed enable a systemto determine said metallization width by subtracting twice saidplacement tolerance from said width of said implanted regions.
 17. Thearticle of manufacture of claim 12, wherein said substrate is a solarcell.